Add support for JXL images which are formatted as an ISOBMFF-based co…

…ntainer (for example used by Adobe when embedding DNG preview/thumbnail files).

See https://github.com/ImageMagick/jpeg-xl/blob/main/doc/format_overview.md#file-format for more information.

vips/foreign.go

@@ -257,10 +257,14 @@ func isJP2K(buf []byte) bool {
 	return bytes.HasPrefix(buf, jp2kHeader)
 }
 
+// As a 'naked' codestream
 var jxlHeader = []byte("\xff\x0a")
 
+// As an ISOBMFF-based container: 0x0000000C 4A584C20 0D0A870A
+var jxlHeaderISOBMFF = []byte("\x00\x00\x00\x0C\x4A\x58\x4C\x20\x0D\x0A\x87\x0A")
+
 func isJXL(buf []byte) bool {
-	return bytes.HasPrefix(buf, jxlHeader)
+	return bytes.HasPrefix(buf, jxlHeader) || bytes.HasPrefix(buf, jxlHeaderISOBMFF)
 }
 
 func vipsLoadFromBuffer(buf []byte, params *ImportParams) (*C.VipsImage, ImageType, ImageType, error) {

vips/foreign_test.go

@@ -149,3 +149,14 @@ func Test_DetermineImageType__JXL(t *testing.T) {
 	imageType := DetermineImageType(buf)
 	assert.Equal(t, ImageTypeJXL, imageType)
 }
+
+func Test_DetermineImageType__JXL_ISOBMFF(t *testing.T) {
+	Startup(&Config{})
+
+	buf, err := os.ReadFile(resources + "jxl-isobmff.jxl")
+	assert.NoError(t, err)
+	assert.NotNil(t, buf)
+
+	imageType := DetermineImageType(buf)
+	assert.Equal(t, ImageTypeJXL, imageType)
+}